Maser P olarization and Magnetic fields during Massive Star Formation

1. Maser Polarization and Magnetic fields during Massive Star Formation W. H. T. Vlemmings ASP Conference Series, Vol. 387, 2008 Do-Young Byun

2. Outline • Theoretical Background • Zeeman Effect • Para- and non-paramagnetic Species • Observational results on HMSF • OH, H2O, Methanol • Summary • KVN Single Dish Polarization

3. Background : Zeeman Effect • Occurs when the degeneracy of magnetic substates is broken under the influence of B field • Zeeman splitting • ~ 103 larger in paramagnetic molecules • OH : paramagnetic • SiO, H2O, CH3OH : non-paramagnetic • Z > D for paramagnetic case • Z : Zeeman splitting, D : Doppler Line Width • Z < D for non-paramagnetic case

4. Large Zeeman Splitting : paramagnetic species • Z > D : no theoretical ambiguity • Zeeman components are well separated and resolved. No significant influence on each other. • B field Strength • Observed splitting directly gives Bcos. •  : angle between B and maser propagation direction • B field direction • Magnetic transitions mF = 1 give rise to Elliptically polarized components (V ~ Bcos, Q ~ -Bsin2). Polarization vector  B • Magnetic transitions mF = 0 give rise to Linearly polarized components (Q ~ Bsin2). Polarization vector || B

5. Small Zeeman Splitting : non-paramagnetic species • Z < D : Complex • B field direction •  < crit ~ 55, Polarization vector || B •  > crit ~ 55, Polarization vector  B • 90 flip of EVPA • Cannot directly determine B field direction • B field strength • B field strength depends on circular pol. fraction and maser saturation level. • need to know saturation level

6. Observational Results on High Mass Star Formation • Most information on small scale magnetic field information has come from OH maser observation • H2O and methanol maser observations are increasing. • SiO maser polarization observations are rare. • Orion IRc2 : magnetic field along the disk (Plambeck+ 2003)

7. HMSF : OH masers • 1.6 GHz, Paramagnetic • Trace ~105 – 108 cm-3 density region • direct measurement of |B| • |B| ~ 1mG , up to ~40mG (Fish&Reid 2007) • Observation toward Cep A (Bartkiewicz+ 2005) • The B direction derived from circular pol. seems to follow ambient B-field, not outflows • B field measurements using 6 and 13GHz OH maser • Consistent with 1.6GHz measurements • Suffer less from Faraday Rotation than 1.6GHz

8. HMSF: H2O masers • First discovery of H2O Zeeman splitting with single dish (Fiebig & Gusten 1989) • High resolution circular pol. • Typically, |B| ~ 15-150mGat 108 – 1011 cm-3 • |B| ~ 650mG in Cep A HW2 (Vlemmings+ 2006b) • Linear Pol • Typically  2% • Rapid change in direction over small scale

9. HMSF: 6.7GHz Methanol masers • Pol. observations of the 6.7G and 12G masers are rare. • Polarization fraction ~ 1.5% • First 6.7GHz polarization map of W3(OH) (Vlemmings+ 2006c) • Better probes of B direction than OH because of less Faraday rotation • Difficult to determine |B| due to Small Zeeman Splitting Pol. Map of W3(OH) - Methanol : Contours and Black lines - OH : Triangles and Red lines

10. HMSF: mm Methanol masers • Lin. Pol. fraction of up to 40% using IRAM 30m. (Wiesemeyer+ 2004) • Lin. Pol detection : 10/14 (Class I), 3/7 (Class II) • Cir. Pol detection towards 2 Class I sources

11. HMSF: Summary • |B|  n0.49 over wide density scale • B remains partly coupled to the gas up to very dense region. • Dynamical importance of B during HMSF process in shaping outflows and jets.

12. 100 MHz 1.4 GHz H-maser GPS 10 MHz 10 MHz Distributor 5 MHz 1 pps ClockSystem 100 MHz Distributor 10 MHz Distributor 1 pps Distributor 1 pps Distributor Control PC GUI Receiver system DAS Clock Field system DigitalE/O Digital O/E LCP Digital Filters Digital Spectro-meter Down Converter Sampler Stokes I,Q,U,V 22 GHz FE Down Converter Sampler RCP WDM Optical MUX WDM Optical DMUX Down Converter Sampler 43 GHz FE Mark5B Down Converter Sampler DIR-1000 Receiver Cabin Observation Building

13. KVN Data Acquisition System • 4 Samplers • 4 Receiver Outputs with 512MHz bandwidth • 2bit quantization • Digital Filter Bank (DFB) • 16x16MHz Streams : • Total Band Width : 256MHz bandwidth • E.g. 1x256MHz, 2x128MHz, 4x64MHz, 8x32MHx, 16x16MHz • Digital Spectrometer (DSM) • FX Type Correlator • Auto and Cross Power Spectrum • Wide : 4x512MHz Streams • Narrow : Max 8 streams w/ 4K channels

14. Continuum Observation • Polarization Observation at K and Q • 3C454.3 Monitoring • MFPOL (Multi-Freq Polarization Observation) • MOGABA (Monitoring of Gamma-ray Bright AGN) • Sensitivity of Linearly Polarization Flux • |Q+jU| ~10mJy (~15mJy) at K(Q) for 15 min obs. • Phase Stability • Random Error < 0.2 (0.3) deg at K (Q) • Systematic Error < 2 deg at K/Q • Instrumental Cross Pol • |dLR – d*RL| < 5% (10%) at K (Q) • Simultaneous Dual Frequency Polarimetry Lee,S.-S.+ in prep

15. To Do • Spectroscopy Polarimetry using DFB+DSM • DFB Quantization Correction, Post Doppler Correction • H2O, CH3OH Single Dish observations • 86, 129GHz Test • VLBI Polarization • Multi-epoch H2O • Calibration Procedure • Noise source • P-Cal System Amp(Q+jU)/I Phs(Q+jU) V/I I/Io